The present invention relates to electrical termination blocks and clamps for clamping wires to the terminal contact(s).
Industrial electrical components, such as controls, switches, timers, relays and other components for machine monitoring, control and operator interfacing, typically have terminal blocks with one or more electrical contacts to couple power and/or interconnect wires. Complex wiring applications, such as factory automation, process and motion control, data acquisition, electrical utility, telecommunications, and HVAC applications, typically use a series of modular terminal blocks to couple the wire leads. These terminal blocks are often mounted on a common metal rail known as a “DIN rail”.
Conventional DIN mounted modular terminal blocks have a thin, non-conductive body that houses an electrical contact and a wire clamping mechanism. Conventional terminal blocks of screw, spring or insulation displacement types are commercially available from Rockwell Automation of Milwaukee, Wis. as the Allen-Bradley “J”, “K” and “L” line of terminal blocks.
The terminal blocks are common in the “feed through” form in which two or more wires are clamped to a metal contact bar inside the terminal block to simply make an electrical connection between the wires. Other terminal blocks have disconnect mechanisms, fuses, thermocouples, diodes, surge protectors and other such components interposed between separate contacts inside the housing for interrupting or otherwise affecting the current path between the wires.
The housings of conventional terminal blocks usually have flexible rail clips that mechanically mount it to the rail. The wire(s) are inserted into the housing and clamped to the contact(s) by a screw or spring inside the housing. The clamp is accessible from outside the housing, but to comply with IP2X “finger-safe” standards, the access opening must be small enough so that a probe approximately the size of a finger cannot make contact with energized parts of the terminal block, namely the contact. Thus, it is conventional to have small funneled openings just large enough to accommodate individual insulated wires. Also, access to the clamping mechanisms is either limited or they are made to be operated by non-conductive parts.
Given the typically large number of wires that must be connected in large industrial applications, it is desirable to make the termination of the wire to the contact as simple and quick as possible. However, the generally enclosed housing of conventional finger-safe terminal blocks can make it difficult to clamp the wire to the terminal contact.
One simple and effective method for terminating the wire to the contact is a “push in” connection in which the exposed end of the wire is clamped to the contact simply by the user inserting the wire into an opening in the terminal block. Existing push in clamp mechanisms typically include a leaf spring that is biased against the contact such that when a wire is inserted therebetween the wire displaces the leaf spring, which in turn provides a biasing force that clamps the wire against the contact. While simple, such systems are only effective for solid wires that have the structural rigidity to displace the leaf spring. Stranded wire lacks sufficient rigidity and thus such systems are not suitable for stranded wire. Another problem with such systems is that it is often difficult to determine whether the wire is securely clamped in place. If the spring fails to clamp the wire adequately, the wire can be dislodged and disrupt the circuit.
Accordingly, an improved wire clamp is desired.